P1398 Misfire Adaptive Numerator at Limit
NAME OF CODEMis-Fire Adaptive Numerator at Limit
WHEN MONITORED
Under closed throttle deceleration engine coolant temperature above 176 degrees, and more than 50 seconds after engine start. The speed at which the deceleration occurs must be sufficient for the given gear range, e.g., above 35 mph in first gear or above 55 mph in high gear.
SET CONDITION
One of the crankshaft position sensor target windows has more than 2% variance from the reference window.
THEORY OF OPERATION
Because of the need for increased engine RPM resolution to detects misfire, machining variation has to be learned. The crankshaft position sensor reference window is continuously compared with the windows for other cylinders. When a variance in one of the other windows is detected, the powertrain control module will learn this variance and make the appropriate RPM adjustment. If the variance exceeds 2%, the trouble code will set.
POSSIBLE CAUSES
- Crankshaft position sensor improperly installed
- Crankshaft position sensor failure
- Crankshaft position sensor flexplate target variation
- Severely worn crankshaft bearings
- Wiring connector
- Powertrain control module failure
- Low compression in one or more cylinders